A light emitting device having an organic electroluminescence element (“electroluminescence” will also be abbreviated as “EL” below) as a light source has been put into practice. Research and development is now being conducted for the purpose of improving light-emission, longevity, and other characteristics.
An organic EL element consumes part of electric power applied when a light emitting device is used, and the element thus generates heat per se. The element lifetime of the organic EL element is reduced when being kept driven at high temperatures. The organic EL element generates a greater amount of heat as its size increases. Therefore, the reduction of the element lifetime due to heat generation during driving is more significant as the element increases in size. For example, when compared with an organic EL element mounted as a light source for a pixel of a display device, an organic EL element mounted on a light emitting device such as a light source for a scanner or an illumination apparatus is far greater in one element size. Therefore, the amount of heat generation by one organic EL element is significantly increased, and the reduction of the element lifetime is noticeable. Then, it is contemplated to prevent a temperature increase of an organic EL element during use and the resultant reduction of element lifetime by providing a heat dissipation mechanism in the device to actively dissipate heat to the outside.
A device including an organic EL element is generally provided with a sealing member for sealing the element. A device configuration is proposed which prevents a temperature increase of an organic EL element by enhancing the heat dissipation performance of the sealing member (for example, see Patent Literature 1). In this conventional technique, in order to enhance the heat dissipation performance of the sealing member, the sealing member has a multilayer structure, which includes a layer having high thermal conductivity (hereinafter also referred to as a heat transfer layer).